Coal cleaning



n- 2, 957 A. A HIRST 2,778,496

COAL CLEANING Filed March 27, 1951 s Shets-Sheet 1 //2 yen for flrfflurfl A ix-.5 I,

Jan. 22, 1957 A. A. HIRST 2,778,496

COAL cuazmmc Filed March 27, 1951 3 Sheets-Sheet 2- Jan. 22, 1957 A. A. HIRST 2,778,496

COAL CLEANING Filed March 2'7, 1951 3 Sheets-Sheet 3 3 FIG. 6.

COAL CLEANING Arthur Algernon Hirst, Bramhall, England, assignor to The National Coal Board, London, England Application March 27, 195i, serialNo. 217,724 Claims priority, application Great Britain March31, 19 50 7 Claims.-- (c1; 2019-12 This invention relates to the separation of coal from its associated impurities and is concerned with washeries employing, but not necessarily exclusively employing, washer boxes of the type -in, which washing is carried out by means of the pulsatory'actionof. water" through a grid supporting a washing bed. ,Such washer boxes are commonly used to wash a relatively large'range of sizesof coal. A washer box may, for instance,.treat all sizes of coal down to zero in a product with a maximum size of 3inches.

Under such conditions the washing of the finer sizes is frequently inefiicient and this is specially so in the case of the washed material smaller than aboutf fl inch. Sometimes the finer sizes of washed coal are retreated in, for example, a rewasher box or, alternatively, in a trough washer, by concentrator tables, or by froth flotation. The present invention provides a simple and inexpensive means of improving the efiiciency of separation of the finer sizes and may be used, either instead of, or in conjunctionwith, any of the methods of retreatment described above.

The very finest sizes of washed coal are rarely, in practice, dewater ed for disposal directly after being discharged from the washer box. Normally such fine sizes are allowed to settle in a vessel provided for the purpose and from which they are fed to dewatering apparatus which may take the form of a fine screen, vacuum filter centrifuge or other appropriate equipment. Frequently .a part 1 of the feed offine coal from the settling vessel by-passes such dewatering apparatus and is returned to the settling vessel. I

When the dewatering apparatus takes the form of a fine screen, material passing the screen may also be returned to the settling vessel.

According to one feature of the present invention a proportion of the finer sizes of WElSi'lCd'COfll is fed from the lower part of a settling vessel backtothe washer box, Whilst a further proportion is dewatered for disposal;

According to a further feature of the invention a proportion of the finer sizes of washed coal withdrawn from a settling vessel are subjected to a separation process and one only of the products of this process is returned to the washer box. V

According to a further feature of the invention the separation process may be a simple washing process or processes.

According to yet a further feature-of the invention the returned product is led to a section of the washer box which is screened from the main flow of water carrying coal therethrough.

The above and other partsof the invention are embodied in preferred alternative methods and inapparatus which will now be described with reference to the accompanying drawings in which:

Fig. 1 is a diagrammatic representation of one washery system embodying the invention; v 1 1 Fig. 2 is a diagrammatic representationof an alternative washery system;

Fig.fl3* is a diagrammatic plan view of a washer box showing the location-of a shielded section;

Figs. 4 and S show alternative forms of simple trough Washersused in thesyst'em illustrated by Fig. 2;

' Fig. 6 is a perspective view of the washer box of 3,

and t Fig. 7 is a diagrammatic representation of a modification ofFig.2. 1 I

In the system illustrated in Fig. 1 a pulsatory action washer box 1 which may be the .well known Baum box, has an inlet 2 foruntreated coal andhas an outlet 2A for the separated fines led to a /2 m/m'dewatering shaker 3, the water outlet 4 ofwhich leads to the usual pump sump 5. Washed coal is removed from the system at 3A.

A pump 6 feeds water and suspended fine material to a I settling vessel 7,which has an overflow 8 returning to the sump 5.

A slurry main 9 leads fromthe settling vessel 7 to a m/m dewatering shaker 10. Washed' coal of finer sizes is removed from the shaker'lfiat 10A. 7

The Water outlet in theshaker 10 is connected as showr through an outlet pipe 11 to the grid of the washer box 1. Preferably, but not essentially, the outlet pipe 11 is led to a section of the'washer grid shielded-from the main flow of water therethrough, as is more fully described below. In any case, 'a proportion of the finest particles still suspended in the outflow from the shaker 10 undergoes a further purging in the main washer box 1, while coarser particles-are dewatered for disposal by the shakers 3 and 10. Impurities and refuse are removed by. elevators from the washer box 1 as shown at 11A.

In the system illustrated in Fig. 2, in which like reference numerals are employed, for like parts, the slurry main 9 incorporates a simple form of trough washer 12.,

By this further feature fine material from the settling vessel is subjected to a washing process whereafter the clean product is dewatered for disposalwhilst the refuse product is returned to the Washer box as hereinbefore described. As the refuse product is returned to the washer box, any fine coal contained in such refuse is recovered in the washer box, consequently, it is unnecessary for the washing process for the fine material from the settling vessel to be such as will give simultaneously a pure coal product and a pure refuse product. Having regard to the fact that the refuse'product may'contain a substantial proportion of fine coal, a fine coal product of relatively low ash content may be obtained when using quite simple apparatus for-thewashing process for the fine material. I

In the arrangement shown'in Fig. 4 a simple form of the trough washer arrangement 12 is obtained by partially blockingthe pipe 9 by inserting 'a weir plate 13 between two sections of the pipe, which is thus converted to a simple formof trough Washer. Fine refuse tends to collect on the upstream side of the weir where an outlet 14 is made in the bottom of the pipe from which impurities, which may contain fine coal, either flow by gravity, or are pumped or otherwise conveyed to the washerv box I. A slidable orifice plate 15 is fitted in the outlet 14 to control the proportion flowing therethrough. I It has been found, in practice, that under the conditions described and in which a pure refuse product is not required, a considerable degree of cleaning is effected even if the weir is omitted.

elevation, it is wedge-shaped, the axis of the wedge being roughly horizontal. Feed enters the wedge-shaped section at apex l6 and there is an outlet 11 for clean coal atthe top of the side opposite the apex, this outlet 'being connected to the dewatering apparatus 10. At the bot- Patented Jam-22, 1957 in the arrangement shown-in Fig. 5 a section of the pipe 9 feeding from the settling vessel to the dewatering apparatus is madein'a form such that, in

tom of the side opposite the apex of the wedge an outlet 18 is provided for impure refuse'which is conveyed to the washer box. The outlet for clean coal, may, but need not, be at a higher level than the inlet for material from the settling vessel. The above are examples of simple devices which may be employed, and, of course, givea satisfactory cleaning effect only because of the ability or" the washer box to retreat the resulting refuse, thereby recover'ing any fine coal which may be contained therein. When making use of such simple devices, it is desirable toprovide means of controlling the rates of discharge the clean coal and/or refuse products. It is to be understood, however, that more elaborate cleaning apparatus may be employed instead of the simple devices described. Even when using a more elaborate process of fines washing, economies result from the fact that the 'refuse product can be allowed to contain coal. This latter consideration, moreover, makes unnecessary close supervision of the fines Washing process.

It will be noted in Fig. 2 that the outlet 14 for the refuse product from the washer 12 is led to a section of the washer box" 1 which is shielded from the "main stream of water which carries coal from right to left.

A shielded section of the washer box 1 may conven iently be obtained, as shown in Figs. 2, 3 and 6, by providing a longitudinal plate C, separated by a relatively small space from the wall dividing the pulsation chamber A from the washing bed B. The pulsation chamber A is provided with four pulsators F. Transverse plates are used, as required to protect the enclosed space from the horizontal water currents used in the main washing process. Fine dirt separated through the washing bed can then fall more or less vertically through the hutch of the washer box without danger of its collecting on the sloping portions of the washer box walls. When the washer box comprises two compartments of which the outlet is the wider (Figs. 3 and 6) the shielded section may be obtained by using a plate C as described above so as to reduce the width of the main washing bed in the outlet compartment to that of the washing bed in the inlet. Such plate need not be carried the full length of the outlet compartment and can extend, say, from its inlet end two thirds of the distance towards the overflow weir of the washer box. If a felspar bed is used in the shielded section the felspar may be retained by a sill D, which may be perforated. Impurities are removed by a worm conveyor E which may discharge them onto the normal refuse elevator 11A.'

It is understood, of course, that where a rewasher box is used, the proportion of fine material fed back for rewashing through the outlet 14 may be returned either to the primary washer box or to the rewasher box. It is further understood that, instead of modifying a primary or rewasher box of normal design by providing a shielded section, either type of washer box may be designed to incorporate a special washing compartment or compartments to fulfill the same function.

From the stream of line material returned to the washer box, impurities are extracted as hereinbefore described, whilst the fine coal joins the main stream of washed coal, and, after passing through the classifying and dewatering screen 3, is eventually returned to the settling vessel. In this fashion impurities are constantly purged from the fine material collecting in the settling vessel, thereby reducing the ash content of the correspond ing dewatered product.

In a modified system of Fig. 2, part of which is indicated in Fig. 7, fines carried on the pipe 9 from the settling vessel 7 (Fig. 2) are subjected to a washing process in the washer 12 whereafter the washed fines are dewatered in the shaker 10 of Fig. 2 as hereinbefore described, but the refuse. product flowing in the outlet 14 instead of being returned to the washer box 1 directly is further subjected to a secondary washing process in a similar washer 19 adapted to produce a relatively pure refuse product which is discarded and a clean product which may not necessarily be free from impurities, and which is returned to the Washer box. In this form of the inventlon the refuse product from the secondary Washing operation may be conveyed along a pipe 20 with its associated water to one of the normal refuse elevators 11A of the washer box 1 whereby the fine refuse is dewatered and becomes mixed with the largerrefuse discarded from the washer box.

in a further variation (not illustrated) fines from the settling vessel are subjected to a Washing process arranged to produceth ree products, namely, washed lines for dewatering and disposal, relatively pure-refuse which is discarded and a middlings product which need not be accurately separated and which is returned to the washer box for retreatment as hereinbefore described.

1 claim: I I

1. Apparatus for the cleani'rig of coal from its associated impurities comprising in combination a pulsatory action washer box a settling vessel for the reception of preliminarily washed fines from said pulsatory action washer box, a slurry main connecting the settling vessel to a dew-atering shaker, separating means arranged in the slurry main providing a refuse product outlet, and a fluid connection between the outlet and a section of the pulsatory action washerbox washing bed shielded from the current carrying the main coal-current therethrough. i

2. Apparatus according to claim 1 in which the separating means comprises a weir arranged in the slurry main and an aperture in the lower part thereof constituting a refuse product outlet.

3. Apparatus according to claim 1 in which the separating means comprises a substantially wedged shaped hollow section whose apex is connected to' the upstream side of the main and whose base'has upper and lower outlet apertures for clean and refuse products respectively.

4. Apparatus according to claim 1 in which shielded section of the washer box washing bed is fitted with a finer gauge grid than the rest of the bed.

5. Apparatus according to claim 1 in which the shielded section of the washer'bed is covered with felspar.

6. Apparatus according to claim 1 in which plates constituting the shield are inclined outwardly from the bottom.

7. Apparatus for cleaning coal from its associated impurities comprising in combination a pulsatory action washer box a settling vessel for the reception of preliminarily washed fines from said pulsatory action washer box, a slurry main connecting the settling main to a dewatering shaker, separating means arranged in the slurry main providing a refuse product outlet, further separating means provided in the refuse product outlet providing a clean-product outlet and a fluid connection between the clean product outlet and a section of the pulsatory action washer box washing bed shielded from the current carrying the main coal stream.

References Cited in the file of this patent UNITED STATES PATENTS 228,465 Lauder June 8, 1880 1,655,849 Stenning Jan. 10, 1928 1,656,271 Downs et al. Jan. 17, 1928 FOREIGN PATENTS 421,890 Great Britain Dec. 27, 1934 OTHER REFERENCES Publication: The Cleaning of Coal, by W. R. Chapman and R. A. Mott, published in London by Chapman & Hall Ltd. 1928. Pages 158, last 4 lines, to page 163 line 9 including Figs. 42, 43, 44. (Division 55.) 

1. APPARATUS FOR THE CLEANING OF COAL FROM ITS ASSOCIATED IMPURITIES COMPRISING IN COMBINATION A PULSATORY ACTION WASHER BOX A SETTLING VESSEL FOR THE RECEPTION OF PRELIMINARILY WASHED FINES FROM SIA D PULSATORY ACTION WASHER BOX, A SLURRY MAIN CONNECTING THE SETTLING VESSEL TO A DEWATERING SHAKER, SEPARATING MEANS ARRANGED IN THE SLURRY MAIN PROVIDING A REFUSE PRODUCT OUTLET, AND A FLUID CONNECTION BETWEEN THE OUTLET AND A SECTION OF THE PULSATORY ACTION WASHER BOX WASHING BED SHIELDED FROM THE CURRENT CARRYING THE MAIN COAL CURRENT THERETHROUGH. 